Various kinds of machines and processes have heretofore been utilized to control or monitor machines, signals or devices.
For example, U.S. Pat. No. 4,607,333 relates to electronic beam exposure apparatus which is controlled by a program which stores the desired circuit pattern, and the data of the computer is supplied to an electrostatic deflector via a digital control circuit, digital to analogue convertors and amplifiers as a voltage which is proportional to the degree of deflection.
Moreover, U.S. Pat. No. 3,573,442 teaches a computer of the sample data type for performing, selecting, computing and combining functions and comprises a single time shared or multiplexed operational amplifier adapted to add and substract analogue signal quantities, through a plurality of input signals and to store the results to a plurality of output switches on memory devices such as capacitors, which results are culled out at proper times as analogue outputs and/or feedback signals.
Furthermore, U.S. Pat. No. 3,548,170 relates to a signal digital computer which takes over functions of all analogue controllers as a process whereby signals from the sensing elements feed into an input multiplexer so that the computer can scan them one at a time, such signals being converted to digital signals having discrete values before entering the computer. The output signals from the computer may be converted to analogue signals or remain digital. U.S. Pat. No. 3548,170 utilizes individual circuits having different electronic components for input and for output, analogue and digital signals.
Finally, U.S. Pat. No. 4,404,625 discloses a programmable logic controller provided with a central control unit consisting of a microcomputer as firmware and input circuit adapted to act as an input interference between the external switches connected to input terminals and the central control unit, and output circuitry controlling external equipment converted to the output terminals in response to the output signal from the central control unit, a program memory for storing the sequence programs set by users as desired, a key input device to be used for monitoring or setting programs, and an indicator for indicating the instructions being sent at the program settings and also instructions being executed during execution of the program. More particularly the input and output circuitry of U.S. Pat. No. 4,404,625 are different and establish their characteristics from discrete components rather than software controlled pulse width modulated power sources.
Each of the foregoing devices have generally been designed to execute a specific monitoring or control function.
Present digital microprocessor technology for control purposes utilize discrete circuitry uniquely designed with specific electronic components to condition each type of input signal from sensing field equipment, and also utilize discrete circuitry uniquely set up with specific electronic components to provide each type of output signal required for controlling the field equipment. Furthermore inputs are handled independently of outputs in present day electronic circuitry.
It is an object of this invention to produce an improved input-output device which utilizes a common set of electronic circuitry repeatedly for a variety of input or output signals.